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<Paper uid="P01-1031">
  <Title>Resolving Ellipsis in Clarification</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Clarification ellipsis (CE), nonsentential elliptical queries such as (1a(i),(ii)) are commonplace in human conversation. Two common readings/understandings of CE are exemplified in (1b,c): the clausal reading is commonly used simply to confirm the content of a particular subutterance. The main function of the constituent reading is to elicit an alternative description or ostension to the content (referent or predicate etc) intended by the original speaker of the reprised subutterance. null  (1) a. A: Did Bo finagle a raise? B: (i) Bo?/ (ii) finagle? b. Clausal reading: Are you asking if BO (of all people) finagled a raise/Bo FI-NAGLED a raise (of all actions) c. Constituent reading: Who is Bo?/What does it mean to finagle?  The issue of whether CE involves an ambiguity or is simply vague is an important one.1a0 2 Clearly, pragmatic reasoning plays an important role in understanding CEs. Some considerations do, nonetheless, favour the existence of an ambiguity. First, the BNC provides numerous examples of misunderstandings concerning CE interpretation,3 where a speaker intends one reading, is misunderstood, and clarifies his original interpretation: null  (2) a. A: ... you always had er er say every foot he had with a piece of spunyarn in the wire/B: Spunyarn?/A: Spunyarn, yes/B: What's spunyarn? b. A: Have a laugh and joke with Dick./ B: Dick?/A: Have a laugh and joke with Dick./B: Who's Dick? 1An anonymous ACL reviewer proposed to us that all CE could be analyzed in terms of a single reading along the lines of &amp;quot;I thought I heard you say Bo, and I don't know why you would do so?&amp;quot;.</Paragraph>
    <Paragraph position="1"> 2Closely related to this issue is the issue of what other readings/understandings CE exhibits. We defer discussion  of the latter issue to (Purver et al., 2001), which provides a detailed analysis of the frequency of CEs and their understandings among clarification utterances in the British National Corpus (BNC).</Paragraph>
    <Paragraph position="2"> 3This confirms our (non-instrumentally tested) impression that these understandings are not on the whole disambiguated intonationally. All our CE data from the BNC was found using SCoRE, Matt Purver's dialogue oriented BNC search engine (Purver, 2001).</Paragraph>
    <Paragraph position="3"> More crucially, the clausal and constituent readings involve distinct syntactic and phonological parallelism conditions. The constituent reading seems to actually require phonological identity. With the resolution associated with clausal readings, there is no such requirement. However, partial syntactic parallelism does obtain: an XP used to clarify an antecedent sub-utterance a1a3a2 must match a1a3a2 categorially, though there is no requirement of phonological identity:  (3) a. A: I phoned him. B: him? / #he? b. A: Did he adore the book. B: adore? / #adored? c. A: We're leaving? B: You?  We are used to systems that will confirm the user's utterances by repeating part of them. These presuppose no sophisticated linguistic analysis. However, it is not usual for a system to be able to process CEs produced by the user. It would be a great advantage in negotiative dialogues, where, for example, the system and the user might be discussing several options and the system may make alternative suggestions, for a system to be able to recognize and interpret a CE. Consider the following (constructed) dialogue in the route- null planning domain: (4) Sys: Would you like to make that trip via Malvern? User: Malvern?  At this point the system has to consider a number of possible intepretations for the user's utterance all of which involve recognizing that this is a clarification request concerning the system's last utterance.</Paragraph>
    <Paragraph position="4"> Appropriate responses might be (5a-c); the sys- null tem should definitely not say (5d), as it might if it does not recognize that the user is trying to clarify its previous utterance.</Paragraph>
    <Paragraph position="5"> (5) a. Yes, Malvern b. Malvern - M-A-L-V-E-R-N c. Going via Malvern is the quickest route d. So, you would like to make that trip  via Malvern instead of Malvern? In this paper we examine the interpretation of CEs. CE is a singularly complex ellipsis/anaphoric phenomenon which cannot be handled by standard techniques such as first order unification (as anaphora often is) or by higher order unification (HOU) on logical forms (see e.g. (Pulman, 1997)). For a start, in order to capture the syntactic and phonological parallelism exemplified in (3), logical forms are simply insufficient. Moreover, although an HOU account could, given a theory of dialogue that structures context appropriately, generate the clausal reading, the constituent reading cannot be so generated. Clark (e.g. (Clark, 1996)) initiated work on the grounding of an utterance (for computational and formal work see e.g. (Traum, 1994; Poesio and Traum, 1997)). However, existing work, while spelling out in great detail what updates arise in an IS as a result of grounding, do not offer a characterization of the clarification possibilities spawned by a given utterance. A sketch of such a characterization is provided in this paper. On the basis of this we offer an analysis of CE, integrated into a large existing grammar framework, Head-Driven Phrase Structure Grammar (HPSG) (specifically the version developed in (Ginzburg and Sag, 2000)). We start by informally describing the grounding/clarification processes and the representations on which they operate. We then provide the requisite background on HPSG and on the KOS framework (Ginzburg, 1996; Bohlin et al., 1999), in which our analysis of ISs is couched. We sketch an algorithm for the process of utterance integration which leads to grounding or clarification. Finally, we formalize the operations which underpin clarification and sketch a grammatical analysis of CE.</Paragraph>
  </Section>
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